Ceramic Metal Circuit Board And Semiconductor Device Using The Same

ABSTRACT

According to one embodiment, a ceramic metal circuit board is a ceramic metal circuit board formed by bonding metal circuit plates to at least one surface of a ceramic substrate. At least one of the metal circuit plates has an area of not less than 100 mm2 and includes a concave portion having a depth of not less than 0.02 mm within a range of 1% to 70% of a surface of the at least one of the metal circuit plates. The concave portion is provided not less than 3 mm inside from an end of the metal circuit plate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation Application of U.S. application Ser.No. 16/546,509 filed Aug. 21, 2019, which is a Continuation of PCTApplication No. PCT/JP2018/010256, filed Mar. 15, 2018 and based uponand claiming the benefit of priority from Japanese Patent ApplicationNo. 2017-057693, filed Mar. 23, 2017, the entire contents of all ofwhich are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a ceramic metal circuitboard and a semiconductor device using the same.

BACKGROUND

Semiconductor elements include power elements represented by IGBT. Theperformance of the power elements is improved year by year. In addition,along with the improvement of the performance of the semiconductorelements, the operation guarantee temperature (junction temperature) israised. As a ceramic metal circuit board used to mount the semiconductorelement, a ceramic metal circuit board with an excellent heat resistantcycle characteristic (TCT characteristic) has been developed to copewith the rise of the operation guarantee temperature. For example, in WO2013/094213 (patent literature 1), the TCT characteristic is improved byoptimizing the side surface shape of a copper circuit board. In patentliterature 1, the reliability is thus improved even if a semiconductorelement whose operating temperature is 170° C. or more is mounted.

A semiconductor device in which a semiconductor element is mounted on aceramic metal circuit board is resin-molded in many cases. The resinmolding makes it possible to improve the productivity and prevent aconduction failure or degradation. For example, in Jpn. Pat. Appln.KOKAI Publication No. 2002-83917 (patent literature 2), concave portionsare provided in the surface of a lead frame, thereby obtaining an anchoreffect to a molding resin.

CITATION LIST Patent Literature

-   Patent literature 1: WO 2013/094213-   Patent literature 2: Jpn. Pat. Appln. KOKAI Publication No.    2002-83917-   Patent literature 3: Jpn. Pat. Appln. KOKAI Publication No. 8-250823-   Patent literature 4: Jpn. Pat. Appln. KOKAI Publication No.    2012-119519

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view showing an example of a ceramic metal circuit boardaccording to an embodiment;

FIG. 2 is a top view showing an example of a metal circuit plateincluding concave portions;

FIG. 3 a is a top view showing an example of the concave portion;

FIG. 3 b is a top view showing another example of the concave portion;

FIG. 4 a is a sectional view showing an example of the concave portion;

FIG. 4 b is a sectional view showing another example of the concaveportion;

FIG. 4 c is a sectional view showing still another example of theconcave portion;

FIG. 4 d is a sectional view showing still another example of theconcave portion;

FIG. 4 e is a sectional view showing still another example of theconcave portion;

FIG. 4 f is a sectional view showing still another example of theconcave portion;

FIG. 5 is a top view showing another example of the metal circuit plateincluding the concave portions;

FIG. 6 is a top view showing still another example of the metal circuitplate including the concave portions;

FIG. 7 is a sectional view showing an example of a semiconductor deviceaccording to the embodiment;

FIG. 8 is a sectional view showing another example of the semiconductordevice according to the embodiment;

FIG. 9 is a top view showing still another example of the metal circuitplate including the concave portions; and

FIG. 10 is a top view showing another example of the ceramic metalcircuit board according to the embodiment.

DETAILED DESCRIPTION

In patent literature 2, fine concave portions are provided on the leadframe. With the fine concave portions, the adhesion to the resin moldingis improved. For example, in FIG. 6 of patent literature 2, asemiconductor element is mounted on the lead frame. A semiconductordevice of patent literature 2 does not use a ceramic substrate. In thedevice that does not use a ceramic substrate, when the operatingtemperature of the semiconductor element becomes high, the durability isinsufficient. In addition, the thermal expansion of a metal circuitboard caused by the rise of the operating temperature of thesemiconductor element becomes large, and the adhesion to the moldingresin is insufficient in the fine concave portions.

On the other hand, patent literature 3 discloses a ceramic circuit boardincluding a ceramic substrate and a metal plate bonded to at least thesurface of the ceramic substrate, in which a plurality of holes areformed inside the outer peripheral edge portion of the metal plate onthe surface side opposite to the bonding surface to the ceramicsubstrate. In patent literature 3, the purpose of providing theplurality of holes inside the outer peripheral edge portion of the metalplate is to release stress to the outer peripheral end of the metalplate.

Patent literature 4 discloses providing, within the range of 0.3 mm to2.0 mm from the semiconductor mounting region end of a copper circuit, athin portion whose thickness d is 20% to 60% of a total thickness D ofthe copper circuit and a brazing material, thereby preventing cracks dueto thermal shock from being generated in a solder layer and a ceramicsubstrate. Additionally, patent literature 4 describes that if the thinportion is provided in a range more than 2.0 mm from the semiconductormounting region end, cracks are generated in the thermal shock test.

The present invention has been made in order to solve such problems, andprovides a ceramic metal circuit board with excellent adhesion to amolding resin, and a semiconductor device.

According to one embodiment, a ceramic metal circuit board formed bybonding metal circuit plates to at least one surface of a ceramicsubstrate, wherein at least one of the metal circuit plates has an areaof not less than 100 mm² and includes a concave portion having a depthof not less than 0.02 mm within a range of 1% to 70% of a surface of theat least one of the metal circuit plates.

A ceramic metal circuit board according to an embodiment is a ceramicmetal circuit board formed by bonding metal circuit plates to at leastone surface of a ceramic substrate, wherein at least one of the metalcircuit plates has an area of not less than 100 mm² and includes concaveportions having a depth of not less than 0.02 mm within a range of 1% to70% of a surface of the at least one of the metal circuit plates, andthe concave portions are formed not less than 3 mm inside from an end ofthe metal circuit plate as well. The concave portions may be formed only3 mm or more inside from the end of the major surface of the metalcircuit plate. The concave portion may be formed both 3 mm or moreinside from the end of the major surface of the metal circuit plate andin a portion less than 3 mm from the end.

FIG. 1 shows an example of the ceramic metal circuit board according tothe embodiment. FIG. 1 is a top view of a metal circuit plate includingconcave portions viewed from the upper side. In FIG. 1 , referencenumeral 1 denotes a ceramic metal circuit board; 2, a ceramic substrate;3, metal circuit plates provided with concave portions; 3-1, a firstmetal circuit plate including concave portion; 3-2, a second metalcircuit plate including concave portions; 4, a metal circuit plate (ametal circuit plate without concave portions); and 5, concave portions.

A plurality of metal circuit plates are bonded to at least one surfaceof the ceramic substrate. The metal circuit plates may be provided ononly one surface of the ceramic substrate, or may be provided on bothsurfaces. If the metal circuit plates are provided on only one surface,a back metal plate serving as a heat dissipation plate may be bonded tothe opposite side. The metal circuit plates are preferably made of oneof copper, a copper alloy, aluminum, and an aluminum alloy.

At least one of the plurality of metal circuit plates is a metal circuitplate having an area of 100 mm² or more. FIG. 2 shows an example of themetal circuit plate including the concave portions. FIG. 2 is a top viewof the metal circuit plate 3 including the concave portions. In FIG. 2 ,reference numeral 3 denotes the metal circuit plate including theconcave portions; and 5, the concave portions. Reference symbol ddenotes a minimum diameter of the concave portion; p, a shortestdistance between the concave portions; L1, a length of a long side ofthe metal circuit plate; and L2, a length of a short side of the metalcircuit plate.

The area of the metal circuit plate is obtained by (length L1 of longside)×(length L2 of short side). If the metal plate has a shape otherthan an oblong shape, the area of the surface is obtained. Variousshapes such as an L shape, an H shape, an S shape, and a circular shapeother than an oblong shape are usable.

In addition, at least one of the metal circuit plates each having anarea of 100 mm² or more is provided with the concave portion. In themetal circuit plate provided with the concave portion, the concaveportion is provided within the range of 1% to 70% of the surface of themetal circuit plate. Additionally, the depth of the concave portions is0.02 mm or more. In addition, the concave portion is formed 3 mm or moreinside from the end of the metal circuit plate as well. That is, theconcave portion is provided not only at the end of the metal circuitplate having an area of 100 mm² or more but also inside. When suchconcave portions are provided in a large circuit plate for which thearea of the metal circuit plate is 100 mm² or more, the anchor effect toa molding resin improves. For this reason, even if the operatingtemperature of the semiconductor element becomes high, troubles such aspeeling of the molding resin can be reduced. In addition, the concaveportion formation area is counted on the surface of one metal circuitplate. At least some of the concave portions need only be provided 3 mmor more inside from the end. In other words, all concave portions may beprovided 3 mm or more inside from the end of the metal circuit plate, orsome of them may be provided within the range less than 3 mm from theend. The area of the major surface of the metal circuit plate on which asemiconductor element or a terminal is mounted is normally 100 mm² ormore. However, as the operating temperature rises, the thermal effect onthe edge of the semiconductor element or the terminal increases. Forthis reason, the molding resin near the edge of the semiconductorelement or the terminal tends to readily peel. When at least some of theconcave portions are formed 3 mm or more inside from the end, peeling ofthe molding resin near the edge of the semiconductor element or theterminal is suppressed. It is therefore possible to suppress peeling ofthe molding resin throughout the metal circuit plate.

If the concave portion formation area is less than 1%, the anchor effectto the molding resin is insufficient. In addition, if the concaveportion formation area is more than 70%, the area to mount thesemiconductor element is short. For this reason, the area to provide theconcave portion needs to fall within the range of 3% to 70% of the metalcircuit plate having an area of 100 mm² or more. In addition, the areawhere the concave portion is provided preferably falls within the rangeof 30% to 70% of the surface of one metal circuit plate. Furthermore,after the semiconductor element or the terminal is mounted, a structureis preferably formed in which the concave portion is provided within therange of 30% to 95% of a semiconductor element non-mounting region otherthan both of a semiconductor element mounting portion and a terminalmounting portion. Hence, in the ceramic metal circuit board before thesemiconductor element or the terminal is mounted, a structure ispreferably formed in which the concave portion is provided within therange of 30% to 95% of the non-mounting region other than both of theregion for the semiconductor element mounting portion and the region forthe terminal mounting portion on the major surface of the metal circuitplate.

FIG. 9 is a top view showing still another example of the metal circuitplate provided with the concave portions. In FIG. 9 , reference numeral3 denotes the metal circuit plate including the concave portions; 5, theconcave portions; 10, a semiconductor element mounting portion; and 11,a terminal mounting portion.

The areas of the semiconductor element mounting portion 10 and theterminal mounting portion 11 can be obtained by observing thesemiconductor device in which the semiconductor element and the like aremounted. The obtained areas are the areas of both of the region for thesemiconductor element mounting portion and the region for the terminalmounting portion. If a solder layer (or a brazing material layer) usedto mount the semiconductor element protrudes, the protruding solderlayer is included in the semiconductor element mounting portion 11. Forthe terminal as well, if the solder layer or brazing material layerprotrudes, it is included in the terminal mounting portion 10. This isbecause if the concave portions are filled with the solder layer orbrazing material layer, the adhesion to the molding resin to bedescribed later cannot be improved.

In addition, since the concave portion is provided in the metal circuitplate whose area is 100 mm² or more, the area to mount the semiconductorelement or the terminal can sufficiently be ensured. In an extremelysmall metal circuit plate or a long metal circuit plate, the area tomount the semiconductor element cannot be ensured. In other words, it issuitable for a ceramic metal circuit board provided with a metal circuitplate having an area of 100 mm² or more.

For the ceramic metal circuit board before the semiconductor element orthe terminal is mounted, a method of obtaining the area ratio of theconcave portion using an engineering drawing is effective.

Additionally, for the ceramic metal circuit board after thesemiconductor element or the terminal is mounted, and the semiconductordevice including the metal circuit board, an upper surface photo ismeasured by an optical microscope. A method of obtaining the area ratioof the concave portion from the upper surface photo is effective.

For the resin-molded semiconductor device, a method using X-rays or amethod of measuring after removing the resin is effective. As the methodusing X-rays, X-ray CT observation is usable. The area ratio of theconcave portion can be obtained using an image of X-ray CT observation.When a 3D image is used, the depth of the concave portion can bemeasured together.

As the method of removing the resin, laser processing, chemical liquidprocessing, or grinding processing can be used. Laser processing is amethod of melting and removing the resin by a laser beam. This method isalso called laser decapsulation. Chemical liquid processing is a methodof dissolving the resin by a chemical liquid. In addition, grindingprocessing is a method of grinding the resin. A method of grinding apredetermined amount and then performing laser processing or chemicalliquid processing is also effective. After the resin is removed, it iseffective to obtain the area ratio of the concave portion by observingwith an optical microscope.

In addition, the depth of the concave portion is 0.02 mm or more. If thedepth of the concave portion is less than 0.02 mm, the anchor effect toa molding resin is insufficient. The depth of the concave portionpreferably falls within the range of 10% to 90% of the thickness of themetal circuit plate. Some of the concave portions may be of apenetration type. That is, both penetration-type concave portion andnon-penetration-type concave portion may be provided in the metalcircuit plate.

In addition, the average minimum diameter d (mm) of the concave portionsviewed from the upper side in a case in which each concave portion has acircular shape or an average minimum groove width W (mm) of the concaveportions viewed from the upper side in a case in which the concaveportions are formed as continuous grooves preferably falls within therange of 0.5 mm to 2 mm. FIGS. 3 a and 3 b are top views of a concaveportion. (a) of FIG. 3 a shows a circular shape, and (b) of FIG. 3 bshows a rectangular shape. The shape of the concave portion is notlimited to these, and various shapes such as an elliptical shape, anoblong shape, a polygonal shape, a star shape, and a wavy shape can beapplied. In the top views of the concave portion, the shortest diagonalline is defined as the minimum diameter d, and the minimum groove widthW is also expressed as d.

In addition, the measurement method of the average minimum diameter d orthe average minimum groove width W includes capturing the metal circuitplate including the concave portions from above by an opticalmicroscope. In one metal circuit plate, the minimum diameter d of eachconcave portion is measured. The result is rounded off to one decimalplace, thereby obtaining the minimum diameter d of the concave portion.The minimum diameters d of all concave portions in one metal circuitplate are measured. Values except the minimum value and the maximumvalue of the individual minimum diameters d are averaged, therebyobtaining the average minimum diameter d. The average minimum groovewidth W is also obtained by the same method.

In addition, if the average minimum diameter d (or the average minimumwidth W) is less than 0.5 mm, the inlet of the concave portion is toosmall, and it may be impossible to sufficiently cause the molding resinto enter. Furthermore, if the average minimum diameter d (or the averageminimum width W) exceeds 2 mm, the molding resin may readily disengage.For this reason, to obtain the anchor effect to the molding resin, theaverage minimum diameter d (or the average minimum width W) of theconcave portions preferably falls within the range of 0.5 mm to 2 mm.Within this range, the minimum diameters d (or the minimum widths W) ofthe individual concave portions may be equal or may be different. Inaddition, the shapes may also be unified, or different shapes may becombined. Furthermore, all the minimum diameters d preferably fallwithin the range of 0.5 mm to 2 mm. Similarly, all the minimum widths Wpreferably fall within the range of 0.5 mm to 2 mm.

In addition, the average shortest distance p between the concaveportions is preferably d/2 (mm) or more. The shortest distance p betweenthe concave portions indicates the shortest of the distances between oneconcave portion and concave portions around it. The shortest distance pbetween the concave portions is also called the pitch of the concaveportions. If the average shortest distance p is less than d/2, thestrength between the pitches between the concave portions may beinsufficient. For example, if the strength between the pitches is shortin a case in which the metal circuit plate is as thick as 0.3 mm or moreor 0.8 mm or more, the adhesion to the molding resin may lower. For theminimum width W as well, the average shortest distance p between theconcave portions is preferably W/2 (mm) or more. In addition, all theshortest distances p between the concave portions preferably satisfy d/2(mm) or more or W/2 (mm) or more.

The measurement method of the average shortest distance p will bedescribed here. The metal circuit plates including the concave portionsare captured from above by an optical microscope. In one metal circuitplate, the shortest distance p between the concave portions is measured.The result is rounded off to one decimal place, thereby obtaining theshortest distance p between the concave portions. The shortest distancesp of all the concave portions in one metal circuit plate are measured.Values except the minimum value and the maximum value of the individualshortest distances p are averaged, thereby obtaining the averageshortest distance p.

In addition, the sectional shape of the concave portion is preferablyone shape selected from a U shape, a V shape, an oblong shape, and acircular shape. FIGS. 4 a, 4 b, 4 c, 4 d, 4 e, and 4 f show examples ofthe concave portion. (c) of FIG. 4 a shows a concave portion whosesectional shape is an oblong shape. (d) of FIG. 4 b shows a concaveportion whose sectional shape is a V shape. (e) of FIG. 4 c shows aconcave portion whose sectional shape is a U shape. (f) of FIG. 4 dshows a concave portion whose sectional shape is a circular shape. (g)of FIG. 4 e shows a concave portion whose sectional shape is striangular shape. (h) of FIG. 4 f shows a shape with a convex portion 22formed at the end (inlet edge) of the concave portion 5.

Of these shapes, the circular shape shown in (f) of FIG. 4 d or thetriangular shape shown in (g) of FIG. 4 e readily improves the bondingstrength to the molding resin. In the concave portion having thecircular shape or the triangular shape, the interior is wider than theinlet of the concave portion. With this structure, the molding resinhardly disengages after solidifying. The oblong shape, the V shape, andthe U shape are structures capable of readily forming a concave portion.Hence, when mass production is taken into consideration, the oblongshape, the V shape, and the U shape are more preferable. The sectionalshapes of the concave portion may be unified in one metal circuit plate,or may be different. Additionally, as shown in (h) of FIG. 4 f , a shapewith the convex portion 22 formed at the opening end edge that is theend of the concave portion 5 may be used. When the convex portion 22 isformed at the end of the concave portion 5, the molding resin can beprevented from being shifted. The concave portion with the convexportion at the opening end edge can be formed by, for example, applyinglaser machining to the metal circuit plate.

The sectional shape of the concave portion is not limited to those shownin FIGS. 4 a, 4 b, 4 c, 4 d, 4 e, and 4 f . A screw groove shape or thelike is also usable.

In addition, the shape of the concave portion may be a groove shape.FIG. 5 shows an example of a metal circuit plate including concaveportions with a groove shape. In FIG. 5 , reference numeral 3 denotesthe metal circuit plate including the concave portions; and 5, theconcave portions. Reference symbol w denotes a minimum width of theconcave portion; and p, the shortest distance between the concaveportions. In FIG. 5 , each concave portion has an oblong shape whenviewed from the upper side. The concave portion with the groove shapeneed not always have the oblong shape, and may have a curved shape suchas an S shape or an M shape. In addition, as the sectional shape, theshapes shown in FIGS. 4 a, 4 b, 4 c, 4 d, 4 e, and 4 f are applicable.The concave portion may combine the circular shape and the groove shape.

In addition, the concave portion may have a continuous groove shape.FIG. 6 shows a top view of a metal circuit plate including concaveportions with a continuous groove shape. In FIG. 6 , reference numeral 3denotes the metal circuit plate including the concave portions; and 5,the concave portions. Reference symbol w denotes the minimum width ofthe concave portion; and p, the shortest distance between the concaveportions. FIG. 6 shows concave portions each having a groove shape, andthe concave portions are communicated with each other and are continuingin a rectangular shape. As described above, the continuous groove shapeindicates a shape formed by connecting concave portions. The continuousgroove shape is not limited to the rectangular shape, and various shapessuch as a polygonal shape, a circular shape, and an elliptical shape canbe used. In addition, the shape can be combined with the shapes shown inFIGS. 3 a and 3 b or FIGS. 4 a, 4 b, 4 c, 4 d, 4 e, and 4 f as describedabove.

In addition, it is preferable that there is at least one portion wheretwo or more concave portions 5 or two or more lines of concave portions5 are arranged outward from the center of the metal circuit plate 3including the concave portions 5. When the concave portions are providedoutward from the center (inside), the molding resin can be preventedfrom being shifted. Examples of the metal circuit plate having theabove-described arrangement are shown in FIGS. 1, 2, 5, 9, and 10 . Forexample, as shown in FIG. 1 or 10 , a portion where three or moreconcave portions or three or more lines of concave portions are arrangedpreferably exists. Here, the center of the metal circuit plate includingthe concave portions is the intersection of two diagonal lines of acircumscribed oblong of the target metal circuit plate.

In addition, the thickness of the metal circuit plate is preferably 0.3mm or more. Furthermore, the thickness of the metal circuit plate ispreferably 0.8 mm or more. When the metal circuit plate is made thick,the heat dissipation properties of the ceramic metal circuit board canbe improved. This is effective in a ceramic metal circuit board in whicha semiconductor element with a high operating temperature is mounted.

In addition, the surface size of the ceramic substrate is preferably 12cm² or more. If the ceramic substrate has an oblong shape, the surfacesize of the ceramic substrate is obtained by long side×short side. Ifthe ceramic substrate does not have an oblong shape, the surface size isobtained by the area of the surface to which the metal circuit plate isbonded. If the ceramic substrate includes a hole for screwing, it is notcounted in the surface size.

If the surface size of the ceramic substrate is 12 cm² (1,200 mm²) ormore, the structure is readily be provided with a plurality of metalcircuit plates. In addition, two or more metal circuit plates eachhaving an area of 100 mm² or more are readily provided. When two or moremetal circuit plates with concave portions are provided, the adhesion tothe molding resin can be made firmer.

Note that the upper limit of the surface size of the ceramic substrateis not particular limited. However, the surface size is preferably 100cm² or less. If the surface size is more than 100 cm², resin molding maybe difficult. For example, in transfer molding, the ceramic metalcircuit board is arranged in a mold, and resin molding is performed forit. If the ceramic metal circuit board is too large, it may be difficultto arrange the ceramic metal circuit board in the mold because of, forexample, an increase in a warp amount of the ceramic metal circuit boardat the early stage or during molding. For this reason, the surface sizeof the ceramic substrate is preferably 12 cm² to 100 cm², and morepreferably 20 cm² to 50 cm². In addition, the ceramic substrate 2 may bea single plate, or may have a three-dimensional structure such as amultilayered structure.

In addition, the ceramic substrate is preferably a silicon nitridesubstrate. As the ceramic substrate, any of an aluminum nitridesubstrate, an alumina substrate, an alumina-zirconia substrate, and asilicon nitride substrate can be applied.

In an aluminum nitride substrate and alumina substrate for generalpurpose use, the three-point flexural strength is about 300 MPa to 450MPa. The alumina-zirconia substrate is a sintered body in which aluminumoxide and zirconium oxide are mixed. The strength of thealumina-zirconia substrate is also about 550 MPa. With a strength of 550MPa or less, if the substrate thickness is 0.4 mm or less, thepossibility that the substrate breaks in molding becomes high, or theTCT (heat cycle) characteristic for a semiconductor device lowers. Inparticular, the durability lowers when the high temperature side of theTCT test is raised to 175° C. or more.

In the silicon nitride substrate, the three-point flexural strength canbe made as high as 600 MPa or more, or 700 MPa or more. There aresilicon nitride substrates having a thermal conductivity of 50 W/m·K ormore, or 80 W/m·K or more. In particular, some silicon nitridesubstrates recently have both a high strength and a high thermalconductivity. In a silicon nitride substrate having a three-pointflexural strength of 600 MPa or more and a thermal conductivity of 80W/m·K or more, the substrate thickness can be decreased to 0.30 mm orless. In particular, when the substrate size is 12 cm² or more, or 20cm² or more, the substrate is preferably a silicon nitride substrate.

Note that the three-point flexural strength is measured by a methodconforming to JIS-R-1601, and the thermal conductivity is measured by alaser flash method conforming to JIS-R-1611.

In addition, the bonding method for the ceramic substrate and the metalcircuit plate is not particular limited, and an active metal method, adirect bonding method, or the like is usable.

Furthermore, as shown in FIG. 7 , the structure may include a back metalplate 8 provided on the back surface of the ceramic substrate 2 withrespect to the surface with the metal circuit plates 3. The back metalplate 8 can be used as a heat dissipation late or a circuit plate.Alternatively, the structure may include concave portions provided inthe back metal plate 8. This is effective when resin-molding the backsurface (the surface provided with the back metal plate 8).Additionally, a grease layer is used when bonding a mounting substrate 9and the back metal plate 8, as will be described later. The adhesion tothe grease layer can be improved by providing the concave portions inthe back metal plate 8.

In addition, of the surfaces (both major surfaces) of the ceramicsubstrate, at least a part of a portion where no metal circuit plate isprovided may be provided with the concave portions. Note that in a casein which the back metal plate is provided, of the surfaces (both majorsurfaces) of the ceramic substrate, at least a part of a surface onwhich no metal circuit plate is provided may be provided with theconcave portions. FIG. 10 shows an example in which the ceramicsubstrate is provided with the concave portions. In FIG. 10 , referencenumeral 1 denotes the ceramic metal circuit board; 2, the ceramicsubstrate; 3, the metal circuit plates provided with the concaveportions; 4, a metal circuit plate without concave portions; 5, theconcave portions; and 12, concave portions provide in the ceramicsubstrate. The first metal circuit plate 3-1 and the second metalcircuit plate 3-2 are provided on one major surface of the ceramicsubstrate 2. In the first metal circuit plate 3-1, concave portionsarranged in two lines outward from the center are formed. On the otherhand, in the second metal circuit plate 3-2, concave portions arrangedin three lines outward from the center are formed.

FIG. 10 shows the surface provided with the metal circuit plates. Theconcave portions 12 are formed at an end of the ceramic substrate 2 inportions of the ceramic substrate 2 where the metal circuit plates thatincludes both of the metal circuit plate 3 provided with the concaveportions and the metal circuit plate 4 that is not provided with theconcave portions are not provided. When the concave portion 12 is formedin the ceramic substrate 2, the adhesion to the molding resin canfurther be improved.

In addition, to avoid lowering of the insulating properties of theceramic substrate 2 caused by the concave portions, the concave portions12 are preferably non-penetration-type concave portions. In addition,the concave portions 12 are preferably provided within the range of 30%to 95% of the surface area of the ceramic substrate 2 that is in directcontact with the molding resin. The minimum diameter d or the minimumwidth W of the concave portion preferably falls within the range of 0.5mm to 2 mm.

The ceramic metal circuit board as described above is suitable for asemiconductor device including a semiconductor element. Thesemiconductor element is preferably mounted on the metal circuit plateprovided with the concave portion. In addition, a plurality ofsemiconductor elements are preferably mounted on the metal circuit plateprovided with the concave portion. Furthermore, the ceramic metalcircuit board is suitable for a resin-molded semiconductor device.

FIG. 7 shows an example of a resin-molded semiconductor device. In FIG.7 , reference numeral 2 denotes the ceramic substrate; 3, the metalcircuit plates provided with the concave portions; 6, semiconductorelements; 7, a molding resin; 8, the metal plate; 9, the mountingsubstrate; and 20, a semiconductor device.

In FIG. 7 , two metal circuit plates provided with the concave portionsare bonded. Two semiconductor elements are mounted on one of the metalcircuit plates, and one semiconductor element is mounted on the other.The semiconductor device according to the embodiment is not limited tosuch a structure, and one semiconductor element or two or moresemiconductor elements can be mounted on the metal circuit plateprovided with the concave portions.

The metal circuit plate provided with the concave portion is a largemetal plate having an area of 100 mm² or more. For this reason, two ormore semiconductor elements can be mounted. On the other hand, eachsemiconductor element serves as a heat generation source. When resinmolding is performed, the resin near the semiconductor element readilypeels due to thermal stress. Hence, when the concave portion isprovided, the resin is difficult to peel.

In particular, this is effective for a semiconductor element having anoperating temperature of 170° C. or more. The operating temperature is aso-called junction temperature. Even if the heat generation amount ofthe semiconductor element increases, peeling of the resin can besuppressed by providing the concave portion. For electrical conductivityof the semiconductor element, wire bonding or a lead frame is used. Ifresin peeling occurs, wire bonding readily breaks. In addition, the leadframe is formed by a metal plate such as a copper plate or an aluminumplate. The metal plate readily thermally expands, and this easily leadsto peeling of the molding resin. Hence, it is effective to preventpeeling of the resin by providing the concave portion.

The semiconductor device shown in FIG. 7 does not include a case. Thesemiconductor device is not limited to such a semiconductor device, anda semiconductor device including a case is also incorporated in thisembodiment. FIG. 8 shows an example. The plurality of metal circuitplates 3 provided with the concave portions are provided at an intervalon one major surface of the ceramic substrate 2 of the semiconductordevice 20. The semiconductor element 6 is mounted on the major surfaceof each metal circuit plate 3. The number of elements mounted may bedifferent for each the metal circuit plate 3. The metal plate 8 isprovided on the other major surface of the ceramic substrate 2. Themetal plate 8 of the ceramic substrate 2 having such a structure isbonded to the mounting substrate 9. A case 21 has a dome shape, and itsopening end is bonded to the surface of the mounting substrate 9. Themolding resin 7 fills the space surrounded by the mounting substrate 9and the case 21. The molding resin 7 is formed by, for example, amolding method using a potting gel. In this case, the case 21 alsoserves as a mold. In addition, the case 21 may be divided into a lid anda side wall.

Additionally, in the ceramic metal circuit board according to theembodiment, the surface size of the ceramic substrate can be as large as12 cm² or more, or 20 cm² or more. For this reason, a number ofsemiconductor elements can be mounted. Since peeling of the moldingresin is suppressed, the reliability of the semiconductor device inwhich a number of semiconductor elements are mounted can be improved.

A method of manufacturing the ceramic metal circuit board according tothe embodiment will be described next. If the ceramic metal circuitboard according to the embodiment has the above-described structure, themanufacturing method is not particularly limited. The following methodcan be used for the manufacture with a high yield.

First, a ceramic substrate is prepared. As the ceramic substrate,various substrates such as a silicon nitride substrate, an aluminumnitride substrate, an alumina substrate, and an alumina-zirconiasubstrate can be applied. The ceramic substrate preferably has athickness of 1 mm or less. If the three-point flexural strength is 600MPa or more, the thickness is preferably 0.4 mm or less. As a substratehaving a high strength, a silicon nitride substrate can be used. Thesilicon nitride substrate preferably has a three-point flexural strengthof 600 MPa or more and a thermal conductivity of 50 W/m·K or more.

A step of providing concave portion in the ceramic substrate isperformed as needed. As the step of providing concave portion in theceramic substrate, shot blasting, laser machining, drilling, or the likecan be performed. The step of providing concave portion in the ceramicsubstrate may be performed after metal plates are bonded.

Next, metal circuit plates are bonded. As a metal circuit plate, acopper plate, a copper alloy plate, an aluminum plate, an aluminum alloyplate, or the like can be used. The metal circuit plate preferably has athickness of 0.3 mm or more, or 0.8 mm or more.

In addition, as the bonding method, an active metal bonding method or adirect bonding method can be used. The active metal bonding method usesa bonding brazing material containing one material or two or morematerials selected from the group consisting of Ti, Zr, Hf, and Si. Theactive metal bonding method can be applied to both an oxide-basedceramic substrate and a nitride-based ceramic substrate.

When one material selected from the group consisting of Ti, Zr, and Hfis used, a brazing material containing silver (Ag) and/or copper (Cu) ispreferable. In addition, indium (In) or tin (Sn) is added as needed.Such a bonding brazing material is suitable for bonding of a copperplate.

When Si is used, a brazing material containing aluminum (Al) ispreferable. Such a bonding brazing material is suitable for bonding ofan Al plate.

The direct bonding method is a method of bonding without using a bondingbrazing material. This is a method suitable for bonding of a copperplate and an oxide-based ceramic substrate. Since no bonding brazingmaterial is used, the cost can be reduced.

In addition, the metal circuit plate to be bonded may be patterned inadvance, or may be a solid plate. If a solid plate is bonded, it ispatterned by an etching process. In addition, a back metal plate isbonded as needed.

In addition, if the metal plate is as thick as 0.3 mm or more or 0.8 mmor more, etching processing may be performed to form a tilting structureon a side surface of the metal plate. When the metal plate side surfacehas a tilting structure, the thermal stress on the bonding end betweenthe metal plate and the ceramic substrate can be reduced, and therefore,the TCT characteristic improves.

Next, a step of providing concave portion in the metal circuit plate isperformed. The metal circuit plate to provide the concave portion has anarea of 100 mm² or more. As the step of providing the concave portion,one of laser machining, drilling, honing, and etching can be performed.

In the laser machining, the laser machining is performed for a portionwhere concave portion should be provided. The minimum diameter or thedepth of the concave portion can be adjusted by controlling the outputor the spot diameter of a laser beam.

In the drilling, the minimum diameter of the concave portion can beadjusted by controlling the diameter of a drill. Additionally, as theshape of the drill, various shapes such as a screw groove shape and aneedle shape can be used. Furthermore, the concave portion depth can beadjusted by the sticking depth of the drill.

In the honing, a mask is attached to the portion where no concaveportions are provided. The honing is performed for portions where themask is not attached. The honing is effective to form a concave portionwith a small depth.

In the etching, an etching resist is provided on the portion where noconcave portions are provided. The etching is performed for portionswhere the resist is not provided. The minimum diameter of the concaveportion can be controlled by the application shape of the etchingresist. In addition, the concave portion depth can be adjusted bycontrolling the etching time. Additionally, the concave portion 5 whosesection has a circular shape as shown in (f) of FIG. 4 d can be formedby the etching. The etching that does not form a through hole is calledhalf etching.

In addition, the portions to provide the concave portion can be providedwithin the range of 1% to 70% of the metal circuit plate surface with anarea of 100 mm² or more. The depth of the concave portion can be 0.02 mmor more. The area to provide the concave portion preferably falls withinthe range of 30% to 95% of one metal circuit plate surface other than asemiconductor element mounting portion region and a terminal mountingportion region.

After the concave portion formation, the mask or the etching resist isremoved.

Next, a step of mounting semiconductor elements is performed. Thesemiconductor elements are provided on the metal circuit plates with theconcave portions. Mounting of the semiconductor elements is performedvia a bonding layer such as solder or a brazing material. Two or moresemiconductor elements may be provided on a metal circuit plate with theconcave portions. In addition, when providing the two or moresemiconductor elements, they may be identical elements or may bedifferent elements.

Next, a step of attaining electrical conductivity of the semiconductorelements is performed. Wire bonding or a lead frame is provided. Inaddition, a semiconductor device (a ceramic circuit board on which thesemiconductor elements are mounted) is mounted on a mounting substrate.In the mounting step of the semiconductor device on the mountingsubstrate, solder, an adhesive, screwing, or the like is used.

Next, a resin molding step is performed. As the resin used in themolding step, an epoxy resin or the like can be used. In addition,various methods such as a transfer method and a compression method areapplied as the molding step. A molding method using a potting gel isalso usable. In recent years, the transfer method is used because of itshigh mass productivity. The transfer molding is a method of heating andsoftening a resin in a plunger, pouring the resin into a mold, andcuring. Since the softened resin is used, gaps in the semiconductordevice with a complex shape can easily be filled with the resin. Inparticular, the interior of each concave portion of the metal circuitplates can easily be filled with the resin. In addition, the massproductivity/productivity is excellent because the molding resin issolidified at once. In the potting step, the case of the module maydirectly be used.

Note that the order of the mounting step of the semiconductor device onthe mounting substrate and the resin molding step may be reversed.

EXAMPLES Examples 1 to 13 and Comparative Examples 1 and 2

Ceramic substrates shown in Table 1 were prepared as ceramic substrates.

TABLE 1 Three- Thermal point Substrate size con- flexural Long side(mm)× ductivity strength short side(mm) × Material (W/m · K) (MPa) thickness(mm) Ceramic Silicon 90 650 60 × 50 × 0.32  substrate 1 nitride CeramicSilicon 80 750 48 × 27 × 0.25  substrate 2 nitride Ceramic Silicon 85700 48 × 27 × 0.20  substrate 3 nitride Ceramic Alumina- 40 550 37 × 27× 0.32  substrate 4 zirconia Ceramic AlN 170 400 37 × 27 × 0.635substrate 5

Next, metal plates were bonded to the ceramic substrates shown in Table1 using an active metal method. If a metal plate is a copper plate,bonding was performed using an Ag—Cu—Sn—Ti-based brazing material. If ametal circuit plate is an Al plate, bonding was performed using anAl—Si-based brazing material. Each main metal plate was etched to form acircuit pattern shown in Table 2. With this step, a ceramic metalcircuit board was formed. The results are shown in Table 2.

TABLE 2 Back metal plate Size: long side Main metal plate (mm) × shortCeramic Size: long side (mm) × side (mm) × substrate Material short side(mm) × thickness (mm) Material thickness (mm) Ceramic metal Ceramic CuOne metal plate having size of 55 × 20 × 0.8 Cu 55 × 45 × 0.8 circuitboard 1 substrate 1 Two metal plates each having size of 55 × 10 × 0.8Ceramic metal Ceramic Al One metal plate having size of 45 × 30 × 0.6 Al55 × 45 × 0.5 circuit board 2 substrate 1 Three metal plates each havingsize of 22 × 13 × 0.6 Ceramic metal Ceramic Cu Two metal plates eachhaving size of 24 × 16 × 0.8 Cu 45 × 24 × 0.7 circuit board 3 substrate2 Three metal plates each having size of 10 × 7 × 0.8 Ceramic metalCeramic Cu Two metal plates each having size of 24 × 16 × 0.8 Cu 45 × 24× 0.7 circuit board 4 substrate 3 One metal plate having size of 10 × 24× 0.8 Ceramic metal Ceramic Cu One metal plate having size of 33 × 15 ×0.5 Cu 35 × 25 × 0.5 circuit board 5 substrate 4 Four metal plates eachhaving size of 7 × 7.5 × 0.5 Ceramic metal Ceramic Cu One metal platehaving size of 33 × 15 × 0.3 Cu 35 × 25 × 0.2 circuit board 6 substrate5 Four metal plates each having size of 7 × 7.5 × 0.3

Concave portions shown in Table 3 were provided in the main metal plateof each of ceramic metal circuit boards 1 to 6. The concave portionswere unified to those shown in Table 3. Ceramic metal circuit boardswith the concave portions are examples, and those without concaveportions are comparative examples. The concave portions were providedonly in metal circuit plates each having an area of 100 mm² or more. Theconcave portions with an oblong sectional shape were formed by lasermachining. The concave portions with a circular sectional shape wereformed by etching. In the ceramic metal circuit boards according to theexamples, concave portions were provided 3 mm or more inside from theend of the metal plate having an area of 100 mm² or more. In the ceramicmetal circuit boards according to Comparative Examples 1 to 6, noconcave portions were provided. In the ceramic metal circuit boardaccording to Comparative Example 7, concave portions were provided onlyat a portion 1 m inside from the end of the metal plate having an areaof 100 mm² or more. The results are shown in Table 3.

TABLE 3 Concave portion Minimum Shortest diameter d Depth Sectionaldistance p Area ratio Ceramic metal circuit board (mm) (mm) shape (mm)(%) Example 1 Ceramic metal circuit board 1 0.5 0.2 Circular 2.0 30Example 2 Ceramic metal circuit board 1 2.0 0.4 Oblong 3.0 40 Example 3Ceramic metal circuit board 2 0.8 0.4 Circular 0.4 70 Example 4 Ceramicmetal circuit board 3 1.0 0.3 Oblong 1.0 40 Example 5 Ceramic metalcircuit board 3 1.4 0.3 Oblong 2.0 35 Example 6 Ceramic metal circuitboard 4 1.5 0.06 Oblong 3.0 30 Example 7 Ceramic metal circuit board 50.5 0.3 Circular 1.0 60 Example 8 Ceramic metal circuit board 6 0.3 0.02Oblong 2.0 5 Comparative example 1 Ceramic metal circuit board 1 —Comparative example 2 Ceramic metal circuit board 2 — Comparativeexample 3 Ceramic metal circuit board 3 — Comparative example 4 Ceramicmetal circuit board 4 — Comparative example 5 Ceramic metal circuitboard 5 — Comparative example 6 Ceramic metal circuit board 6 —Comparative example 7 Ceramic metal circuit board 1 0.5 0.2 Circular 50.3

Ceramic metal circuit boards in which the concave portions have a grooveshape shown in Table 4 are Examples 9 to 11. In Examples 9 and 10, theconcave portions are grooves with an oblong upper surface shape. InExample 11, two continuous grooves each having a rectangular outlineshape are provided. The concave portions were unified to those shown inTable 4.

TABLE 4 Concave portion Minimum groove Shortest width W = d DepthSectional distance p Area ratio Ceramic metal circuit board (mm) (mm)shape (mm) (%) Example 9 Ceramic metal circuit board 1 0.6 0.5 Circular0.5 40 Example 10 Ceramic metal circuit board 1 0.6 0.5 Oblong 0.8 35Example 11 Ceramic metal circuit board 3 1.0 1.0 Circular 2 60

Two semiconductor elements were mounted on a metal circuit plate withconcave portions in each of the ceramic metal circuit boards accordingto the examples and the comparative examples. Next, wire bonding wasperformed. After that, resin molding was performed by the transfermolding method. Semiconductor devices according to the examples and thecomparative examples were thus formed. Additionally, in thesemiconductor device according to each example, in the metal circuitplate with the concave portions, a concave portion formation area in asemiconductor element non-mounting region other than both of asemiconductor element mounting portion and a terminal mounting portionwas obtained. The results are shown in Table 5.

TABLE 5 Concave portion formation area in semiconductor elementnon-mounting region other than semiconductor element mounting regionExample 1 50 Example 2 60 Example 3 80 Example 4 55 Example 5 60 Example6 45 Example 7 75 Example 8 30 Example 9 55 Example 10 45 Example 11 65

Next, a resin adhesion strength and a TCT test were performed for theceramic metal circuit boards according to the examples and thecomparative examples. In the resin adhesion strength, the bondingstrength of the molding resin on the metal circuit plate with theconcave portions was measured by a shear test. Additionally, in the TCTtest (heat cycle test), −40° C.×30 min→room temperature (25° C.)×10min→175° C.×30 min→room temperature (25° C.)×10 min was defined as onecycle, and the presence/absence of peeling of the molding resin after300 cycles was measured. As for peeling of the molding resin, thepeeling area ratio between the resin and the main metal plate that isthe metal circuit plate provided with the concave portions was evaluatedby ultrasonic inspection (SAT). The peeling area ratio was obtained bypeeling area ratio (%)=(area of resin peeling/area of metal circuitplate with concave portions)×100. The results are shown in Table 6.

Additionally, as Example 12, a ceramic metal circuit board formed byproviding concave portions in the ceramic substrate of the ceramic metalcircuit board according to Example 1 was prepared. In addition, asExample 13, a ceramic metal circuit board formed by providingnon-penetration-type concave portions in the ceramic substrate of theceramic metal circuit board according to Example 8 was prepared. For theconcave portions provided in the ceramic substrates, a diameters d ofthe concave portions were unified to 1 mm. In addition, the concaveportions in each ceramic substrate were formed to be 30% of the area ofa portion other than a region where a metal plate was bonded. They wereprovided outside the ceramic substrate.

TABLE 6 Adhesion: Peeling shear area strength MPa) ratio (%) Example 1 60 Example 2 7 0 Example 3 9 0 Example 4 7 0 Example 5 7 0 Example 6 6 0Example 7 7 0 Example 8 4 5 Example 9 10 0 Example 10 9 0 Example 11 9 0Example 12 8 0 Example 13 7 2 Comparative Example 1 2 15 ComparativeExample 2 2 10 Comparative Example 3 1 12 Comparative Example 4 1 10Comparative Example 5 1 5 Comparative Example 6 1 8 Comparative Example7 2 12

As is apparent from the table, for each ceramic metal circuit board withthe concave portions, satisfactory results were obtained in both theshear strength and the peeling area. For this reason, the ceramic metalcircuit boards according to the examples are suitable for asemiconductor device to be resin-molded.

Additionally, if the concave portions were provided only at the end (1mm from the end) of the metal circuit plate, as in Comparative Example7, the adhesion strength to the molding resin was insufficient.

In each of Examples 12 and 13 in which the concave portions wereprovided in the ceramic substrate, the performance was improved. Thisshows that providing the concave portions in the ceramic substrate isalso effective.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

1. A ceramic metal circuit board formed by bonding metal circuit platesto at least one surface of a ceramic substrate, wherein at least one ofthe metal circuit plates has an area of not less than 100 mm² andcomprises a concave portion having a depth of not less than 0.02 mmwithin a range of 1% to 70% of a surface of the at least one of themetal circuit plates, and the concave portion is provided not less than3 mm inside from an end of the at least one of the metal circuit plates,and wherein a sectional shape of the concave portion is at least oneshape selected from a triangular shape or a shape with a convex portionformed at an inlet edge of the concave portion.
 2. The ceramic metalcircuit board according to claim 1, wherein an area to provide theconcave portion falls within a range of 3% to 70% of one metal circuitplate surface.
 3. The ceramic metal circuit board according to claim 2,wherein the area to provide the concave portion falls within a range of30% to 95% of one metal circuit plate surface other than a semiconductorelement mounting portion region and a terminal mounting portion region.4. The ceramic metal circuit board according to claim 1, wherein thedepth of the concave portion falls within a range of 10% to 90% of athickness of the metal circuit plate.
 5. The ceramic metal circuit boardaccording to claim 1, wherein an average minimum diameter d (mm) or anaverage minimum groove width w of the concave portion viewed from anupper side falls within a range of 0.5 mm to 2 mm.
 6. The ceramic metalcircuit board according to claim 1, wherein an average shortest distancep between concave portions is not less than d/2 (mm) or not less thanw/2 (mm).
 7. The ceramic metal circuit board according to claim 1,wherein a thickness of the metal circuit plate is not less than 0.3 mm.8. The ceramic metal circuit board according to claim 1, wherein asurface size of the ceramic substrate is not less than 12 cm².
 9. Theceramic metal circuit board according to claim 1, wherein the ceramicmetal circuit board has a structure including a back metal plateprovided on a side opposite to a surface of the ceramic substrate onwhich the at least one of the metal circuit plates is provided.
 10. Theceramic metal circuit board according to claim 9, wherein the ceramicmetal circuit board has a structure including a concave portion providedin the back metal plate.
 11. The ceramic metal circuit board accordingto claim 1, wherein the ceramic substrate comprises a silicon nitridesubstrate.
 12. The ceramic metal circuit board according to claim 1,wherein at least a part of the surface of the ceramic substrate, whichexcludes a portion where the at least one of the metal circuit plates isprovided, comprises a concave portion.
 13. A semiconductor deviceincluding a semiconductor element provided on a metal circuit plateprovided with a concave portion of the ceramic metal circuit board ofclaim 1 comprises a concave portion.
 14. The semiconductor deviceaccording to claim 13, wherein semiconductor elements are provided onthe at least one of the metal circuit plates provided with the concaveportion.
 15. The semiconductor device according to claim 13, wherein ajunction temperature of the semiconductor element is not less than 170°C.
 16. The semiconductor device according to claim 13, wherein thesemiconductor device is resin-molded.